This invention relates generally to a filter-coefficient conversion system, and more particularly to a filter-coefficient conversion system for converting filter coefficients used for digital filters that can analyze and display biological signals, such as a brain wave, essentially in real time.
Digital filters are used for extracting the spectral distribution of biological signals, as described in U.S. patent application Ser. No. 07/794,526 previously proposed by the present Applicants, for example.
The conceptual block diagram of digital filter is shown in FIG. 6. In FIG. 6, .DELTA.T refers to a time-delay element, x to a multiplication element, and + to an addition element, respectively. The block diagram shown in FIG. 6 is concerned with a digital filter configured with wired circuits. In practice, spectrum is calculated by computer processing using coefficients a.sub.ij held in a filter-bank table.
FIG. 1 shows the configuration of a filter-bank table. By using the filter coefficients, the instantaneous power at time k at which a digitized time-series input signal {X.sub.i } is input to the j-th filter can be obtained by the following equation in an FIR filter. ##EQU1##
It follows from this that assuming that the integration weight coefficient is W(k) (k=-1, - - -, 1), the power P(j) when the time-series input signal {X.sub.i } is input can be obtained from the following equation, and thus, the power spectrum for a desired frequency band can be obtained. ##EQU2##
To obtain a power spectrum in this manner, however, ##EQU3## times of multiplications must be performed, as can be seen from Equations (1) and (2) above. This results in the need for a long multiplication time, posing a problem that when signal components in a desired frequency band are extracted from the above-mentioned biological signals, the number of multiplications is too many to be processed in real time with a small computer of a size of 1-chip microcomputer.